The centrifuge is one member of a substantial class of tools and equipment used in the laboratory, and it plays an important role in a wide variety of applications, including clinical applications or biochemical research. It is of particular importance in the field of molecular biology, where everything from tissue cultures to micromolecules is the focus of study.
For example, it is known to use a centrifuge to separate the liquid and solid phases of blood using a centrifuge. The preparation of a viable culture of white blood cells prefatory to culturing those cells for the purpose of preparing a karyotype, for example, requires that all fluids and other cellular components be removed from a blood sample. It is not uncommon, then, for a technician to add substances that will lyse the red blood cells, and then spin the blood sample in a centrifuge to separate the liquid and solid components. Liquid components, i.e., the supernatant, tend to rise to the top. Solid components tend to aggregate at the bottom of the tube in a mass commonly called a precipitate or a "pellet".
If the pellet is of interest, the technician may then pipet the supernatant away, or remove it by some other means such as pouring or wicking it away, in a manner that does not disturb the pellet. If the supernatant is of interest, it is preferably removed in a way that does not disturb the pellet and cause re-mixing of the solid and liquid phases.
Conventional centrifuge tubes, particularly microcentrifuge tubes, do not always facilitate the separation of pellet and supernatant. In particular, pelleted material in molecular biology is frequently very small and may even be invisible to the naked eye. Because the molecule(s) of interest is often a very small component of the overall sample under study, it is not unusual to require the removal of great volumes of supernatant. Since the pellet must often be suspended and re-suspended in an effort to "purify" or "concentrate" it as much as possible, it is of critical importance to retain as much of the pellet as possible when subjecting it to serial suspensions. Similarly, if one is attempting to obtain a sample of supernatant with minimal or no suspended particles, a device or method that would improve one's chances of obtaining a purer sample would be extremely valuable.
While liquid materials may be poured off, supernatants are typically removed via the use of suction devices. These devices tend to have pipette-like tips and may be operated manually or with the assistance of vacuum devices. Use of suction devices creates some difficulties where, as is often the case, the pellet is small and difficult to see. The pelleted material at the bottom of the tube is easily dislodged, and may become re-suspended in the supernatant or lost altogether. These difficulties are further exacerbated by the extremely smooth interior surfaces of centrifuge tubes.
Therefore, it is an object of the present invention to provide a tube for use in centrifugation which will not interfere with the formation of the precipitate (pellet) and supernatant phases, but which will also facilitate the separation of those phases with a minimum loss of material. It is a further object of the present invention to provide a method for making such a tube. Another object of the present invention is to provide a centrifuge tube which is easy to use and cost-effective to manufacture.